Background Individuals with asthma are more atopic than the general population, but few reports have quantified this association, i.e. the proportion of asthma in the community due to specific immunoresponse.

We aimed to determine the population attributable risk of asthma in the community due to atopy, and the quantity and quality of specific immunoresponses to common aeroallergens involved.

Methods We used data from a cross-sectional study in a random sample of the general Spanish population, 20-44 years old, from five areas.

In all, 1816 participants were given a symptoms questionnaire, a methacholine challenge and were assessed for atopy.

Bronchial responsiveness (BR) was defined as a >=20% fall in forced expiratory volume in one second (FEV1) after methacholine.